As described, for example, in Kokai (Japanese Unexamined Patent Publication) No. 2001-212583, treatment of the livestock waste in a composite lagoon-type clarification tank is known.
Also, in a wastewater purification system for purifying livestock waste-containing wastewater by a batch activated sludge process, when permanent sensors for DO (dissolved oxygen in water), ORP (oxidation-reduction potential) and pH (hydrogen ion concentration) are provided and the data are continuously recorded, there appear sensor data waveforms having constant patterns according to the difference in the conditions such as the amount and quality of activated sludge, the inflow load, the aeration output and aeration time, and the accumulation degree of ammonia, nitrous acid and nitric acid in the reaction tank. Conventionally, an automatic control system where a field supervisor modifies the operating program thereof on the basis of the meaning of such a waveform or where the aeration is automatically stopped when a numerical value of a mater relay corresponding to DO or ORP is reached to a certain numerical value, has been employed.
However, the meter relay system of controlling aeration only by the numerical value of DO, ORP or pH has a problem that good control cannot be satisfactorily obtained.
The sensor data waveforms may be classified into patterns according to the above-described various conditions, but the field supervisor is required to have considerable experience and training to allow appropriate judgment and if this judgment is incorrect, underaeration, overaeration or the like results, and a predetermined function cannot be maintained. Incidentally, when the function cannot be maintained, a professional engineer is called to the field, but in the case where the professional engineer is located at a remote site, the response is not quick in many cases. Furthermore, because no means for automatically judging the level of adequacy of the aeration control is available, unnecessary power consumption and failure to satisfactorily fulfill the function occur.